The present invention disclosed herein relates to a thermoelectric device and a method of forming the same, and a temperature sensing sensor and a heat-source image sensor using the same, and more particularly, to a thermoelectric device, a temperature sensing sensor, and a heat-source image sensor using a nanowire.
A thermoelectric device, which converts thermal energy into electrical energy, belongs to one of representative technology fields that can satisfy recent energy and eco-friendly policies. The heat source of the thermoelectric device may include all kinds of heat such as solar heat, automobile waste heat, earth heat, body heat, and radioactive heat on earth.
The thermoelectric effect was discovered by Thomas Seebeck in the nineteenth century. Seebeck connected bismuth and copper, and disposed a compass therein. Seebeck demonstrated the thermoelectric effect for the first time by showing that a current is induced due to a temperature difference when one side of bismuth is heated to a high temperature, and a magnetic field generated due to the induced current allows the compass to operate.
A ZT (figure of merit) value is used as an indicator for estimating the thermoelectric efficiency. The ZT value is directly proportional to the square of the Seebeck coefficient and electric conductivity, and is inversely proportional to thermal conductivity. These are highly dependent on the inherent characteristics of a material. In the case of metal, since the Seebeck coefficient value is very low as a level of about several μN/K, and there is a proportional relation between the electric conductivity and the thermal conductivity according to the Wiedemann-Franz law, the ZT value may be impossible to rise when metal is used. On the other hand, thermoelectric devices that employ body heat and radioactive heat as a heat source have come to the market by diligent studies by scientists on semiconductor materials. However, the market size is still small. Examples of materials for thermoelectric devices that have been commercialized include Bi2Te3 used at normal and medium temperatures, and SiGe used at a high temperature. Bi2Te3 has a ZT value of about 0.7 at a normal temperature, and has a maximum ZT value of about 0.9 at a temperature of about 120° C. SiGe has a ZT value of about 0.1 at a normal temperature, and has a maximum ZT value of about 0.9 at a temperature of about 900° C.
Studies based on silicon that is a basic material in the semiconductor industry are also attracting attention. Since silicon has a ZT value of about 0.01 due to its high thermal conductivity of about 150 W/m·K, it has been known that it is difficult to utilize as a thermoelectric device. However, it has been recently reported that thermal conductivity of silicon nano-line grown by a chemical vapor deposition can be reduced to about 0.01 times or less, and therefore the ZT value approaches about 1.
However, the integration and commercialization of a silicon nano-line-based thermoelectric device utilizing a typical technology are confronted by difficulties, one of which may be absence of a nano-line manufacturing method that enables mass production. Most manufacturing methods include individually growing in a furnace by utilizing a catalyst or non-catalyst method. However, such an individual growing method has the following two limitations. First, nano-lines may not be consistently grown in one direction, and some nano-lines may be grown in an undesired direction to obstruct the growth of other nana-lines. This becomes a significant limitation in obtaining high-quality nano-lines. Second, nano-lines individually grown in a furnace are moved to a device, and then have to be attached to the device. That is, since the nano-lines and the device are not integrally manufactured, mass production is difficult to achieve. Also, since much time is spent in this course, the production cost considerably increases.